1. Field of the Invention
The present invention relates to a reconstructing process method for a secondary differential value image, an image contour emphasizing process method based on the reconstructing process method, and a thermal transfer printer for performing recording based on the contour emphasizing process method and, more particularly, to a reconstructing process method, for a secondary differential value image, which corrects blurring at a contour portion of an original image to perform recording, an image contour emphasizing process method based on the reconstructing process method, and a thermal transfer printer for performing recording based on the contour emphasizing process method.
2. Description of the Related Art
Conventionally, a thermal transfer printer which comprises an image scanner serving as a means for reading information of an original such as an image or a document and has an easy copy function for performing a conversion process for the information loaded by the image scanner as recording data and causing a recording mechanism having a recording head to perform recording based on the recording data has been proposed.
When such a conventional thermal transfer printer comprising an image performs a conversion process image information of an original as recording data, in order to perform recording such that the contour portion of the original image, i.e., an edge is emphasized (made sharp), a contour emphasizing process for an image is performed.
A conventional contour emphasizing process for an original image will be described below with reference to FIG. 27.
FIG. 27A shows a function f(x) representing a variable density section of an edge of an original image; FIG. 27B shows the primary differential df/dx of the function f(x), and FIG. 27C shows the secondary differential d.sup.2 f/dx.sup.2 of the function f(x). In the conventional technique, as shown in FIG. 27D, a contour emphasizing process represented by the process of subtracting the function in FIG. 27C from the function in FIG. 27A, i.e., f(x)-d.sup.2 f/dx.sup.2 is performed. When such a process is performed, as shown in FIG. 27C, the secondary differential d.sup.2 f/dx.sup.2 has positive and negative values before and after the slope of the edge. For this reason, a change in density of the edge can be enlarged by the function f-d.sup.2 f/dx.sup.2 in FIG. 27D.
Such an effect is similar to the Mach effect observed by a sense of a person. When several belt-like patterns having different brightnesses are seen, a person generally feels as if the boundary between belts in which density changes in a step-like manner is temporarily darkened and then brightened again.
However, in an image conventional contour emphasizing process method and a thermal transfer printer for performing recording based on this method, as shown in FIG. 27D, an edge emphasizing process output value is overshot or undershot. For this reason, if an original image is a blurred image, in order to emphasize the contour portion of the original image to obtain a sharp contour, the contour unnaturally appears in the actual recorded image, or the peripheral portion of the contour portion is blurred.